/*
 * Copyright 2013-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.cloud.cli.compiler;

import java.util.ArrayList;
import java.util.List;

/**
 * TAKEN FROM GRADLE (https://github.com/gradle/gradle/blob/master/subprojects/base-services/src/main/java/org/gradle/api/JavaVersion.java)
 *
 * An enumeration of Java versions.
 * Before 9: https://www.oracle.com/technetwork/java/javase/versioning-naming-139433.html
 * 9+: https://openjdk.java.net/jeps/223
 */
enum JavaVersion {
	VERSION_1_1, VERSION_1_2, VERSION_1_3, VERSION_1_4,
	VERSION_1_5, VERSION_1_6, VERSION_1_7, VERSION_1_8,
	VERSION_1_9, VERSION_1_10,
	/**
	 * Java 11 major version.
	 *
	 * @since 4.7
	 */
	VERSION_11,

	/**
	 * Java 12 major version.
	 *
	 * @since 5.0
	 */
	VERSION_12,

	/**
	 * Higher version of Java.
	 * @since 4.7
	 */
	VERSION_HIGHER;
	// Since Java 9, version should be X instead of 1.X
	// However, to keep backward compatibility, we change from 11
	private static final int FIRST_MAJOR_VERSION_ORDINAL = 10;
	private static JavaVersion currentJavaVersion;
	private final String versionName;

	JavaVersion() {
		this.versionName = ordinal() >= FIRST_MAJOR_VERSION_ORDINAL ? getMajorVersion() : "1." + getMajorVersion();
	}

	/**
	 * Converts the given object into a {@code JavaVersion}.
	 *
	 * @param value An object whose toString() value is to be converted. May be null.
	 * @return The version, or null if the provided value is null.
	 * @throws IllegalArgumentException when the provided value cannot be converted.
	 */
	public static JavaVersion toVersion(Object value) throws IllegalArgumentException {
		if (value == null) {
			return null;
		}
		if (value instanceof JavaVersion) {
			return (JavaVersion) value;
		}
		String name = value.toString();
		int firstNonVersionCharIndex = findFirstNonVersionCharIndex(name);
		String[] versionStrings = name.substring(0, firstNonVersionCharIndex)
				.split("\\.");
		List<Integer> versions = convertToNumber(name, versionStrings);
		if (isLegacyVersion(versions)) {
			assertTrue(name, versions.get(1) > 0);
			return getVersionForMajor(versions.get(1));
		}
		else {
			return getVersionForMajor(versions.get(0));
		}
	}

	/**
	 * Returns the version of the current JVM.
	 *
	 * @return The version of the current JVM.
	 */
	public static JavaVersion current() {
		if (currentJavaVersion == null) {
			currentJavaVersion = toVersion(System.getProperty("java.version"));
		}
		return currentJavaVersion;
	}

	private static JavaVersion getVersionForMajor(int major) {
		return major >= values().length ? JavaVersion.VERSION_HIGHER : values()[major - 1];
	}

	private static void assertTrue(String value, boolean condition) {
		if (!condition) {
			throw new IllegalArgumentException("Could not determine java version from '" + value + "'.");
		}
	}

	private static boolean isLegacyVersion(List<Integer> versions) {
		return 1 == versions.get(0) && versions.size() > 1;
	}

	private static List<Integer> convertToNumber(String value, String[] versionStrs) {
		List<Integer> result = new ArrayList<Integer>();
		for (String s : versionStrs) {
			assertTrue(value, !isNumberStartingWithZero(s));
			try {
				result.add(Integer.parseInt(s));
			}
			catch (NumberFormatException e) {
				assertTrue(value, false);
			}
		}
		assertTrue(value, !result.isEmpty() && result.get(0) > 0);
		return result;
	}

	private static boolean isNumberStartingWithZero(String number) {
		return number.length() > 1 && number.startsWith("0");
	}

	private static int findFirstNonVersionCharIndex(String s) {
		assertTrue(s, s.length() != 0);

		for (int i = 0; i < s.length(); ++i) {
			if (!isDigitOrPeriod(s.charAt(i))) {
				assertTrue(s, i != 0);
				return i;
			}
		}

		return s.length();
	}

	private static boolean isDigitOrPeriod(char c) {
		return (c >= '0' && c <= '9') || c == '.';
	}

	/**
	 * Returns if the version is Java 11 compatible.
	 *
	 * @since 4.7
	 */
	public boolean isJava11Compatible() {
		return this.compareTo(VERSION_11) >= 0;
	}

	@Override
	public String toString() {
		return this.versionName;
	}


	public String getMajorVersion() {
		return String.valueOf(ordinal() + 1);
	}
}